Is postdecisional dissonance functional?

Posted on July 25, 2010


Last semester I taught Judgement and Decision Making using the Scott Plous book The Psychology of Judgment and Decision Making. I found the book quite frustrating in that it followed the “rhetoric of irrationality” that is currently favoured within JDM right up to the last chapter where it took a more critical view of this stance. Discussing a number of the various ‘biases’ proposed by JDM researchers with my students it struck me that it should be possible to model a lot of the situations to find the conditions under which the ‘biases’ are actually functional (I am writing ‘biases’ inside scare quotes as in most cases JDM researchers fail to think of biases as coming along with heuristics and task environments).

One example of just such a potentially modelable phenomenon is that of postdecisional dissonance. In the Plous book it is explained in terms of cognitive dissonance, which is a mechanism for maintaining a relatively coherent set of beliefs. Yet, it seems that there is an alternative explanation. The first example of postdecisional dissonance Plous talks about is from Knox and Inkster 1968 who showed that people tend to be much surer that ‘their’ horse will win after they have bet upon it as opposed to just before betting. The same effect was found in the case of voting by Frenkel and Doob in 1976.

The obvious thought is that in some cases such an increase in belief that the chosen alternative is the best may help to improve the choice. For example, it is quite likely that people just after getting married are much surer that their new spouse is the right one than just before marrying. Being much more certain of one’s choice in that situation is likely to lead to the investment of additional effort into making the marriage a success. But, even in cases where this effect is not likely to take place, it is possible to think of a functional explanation.

Consider a possible scenario in which it is possible to change one’s preference after the initial choice but only at some cost. Such situations are very common. For example, having bought a particular brand of television one might go back to the store and return the recently purchased set in order to buy a different one.  Consider further the possibility that one is in the possession of incomplete information and that there are at least two alternatives that are almost equally attractive. This is a condition that, given bounded rationality, is going to be the case very often. Indeed, the cases where one of the alternatives is much better than the others are not going to be very interesting in terms of decision making. In this kind of situation it is possible to end up vacillating between the available alternatives as new information comes in affecting their perceived utility or as we focus upon particular aspects of the alternatives making them alternatively appear superior. While this situation is bad enough prior to an initial choice being made, it is potentially downright disastrous afterwards. One could, potentially, end up repeatedly changing one’s preference and paying the cost of switching.

Postdecisional dissonance could be a means to stop that from occurring. The mechanism is that, once a choice is made, the chosen alternative’s subjective expected utility is increased in order to make it unlikely that random fluctuations in the SEU will lead to the unchosen alternative coming to be perceived as superior. At the same time, should any significant change in the SEU of either alternative occur, the mechanism allows for a change in the choice. In effect, once a choice is made, that choice will only be second guessed if there is a significant change in the SEUs, hopefully sufficient to outweigh the cost of changing one’s mind. Each of the various variables I have mentioned ought to be capable of being modelled using a fairly simple set-up making it possible to see just what sorts of conditions are necessary for postdecisional dissonance to be functional in this way. My suspicion is that these conditions are going to be fairly common.

While this is a model of just one of the very many mechanisms that Plous mentions, it seems to me that it ought to be possible to pursue this line of attack for many of the others. I wonder if this kind of thing is actually being done by anyone. I should ask my KLI colleague, Joanna Bryson, as she is into modelling and, therefore, may be able to give me an answer.